Much attention has been given to a gain cell semiconductor device that is capable of reading and writing data by using a combination of a transistor in which silicon (Si) is used for a semiconductor layer and a transistor in which a metal oxide is used for a semiconductor layer (see Patent Documents 1 to 3).
In recent years, with the increase in the amount of data dealt with, semiconductor devices having a larger storage capacity have been required. To increase storage capacity per unit area, stacking memory cells is effective (see Patent Document 4). Stacking memory cells can increase storage capacity per unit area in accordance with the number of the stacked memory cells.